From 4b265ca213d066897db3a2333a3ac1420e8a480f Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Mon, 22 Jul 2013 15:05:39 +0200
Subject: Added eta-expansion.

Also: made RepeatedParamTypes aliases of their underlying types, in order to avoid any incompatibilities.
---
 src/dotty/tools/dotc/typer/EtaExpansion.scala | 109 ++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 src/dotty/tools/dotc/typer/EtaExpansion.scala

(limited to 'src/dotty/tools/dotc/typer/EtaExpansion.scala')

diff --git a/src/dotty/tools/dotc/typer/EtaExpansion.scala b/src/dotty/tools/dotc/typer/EtaExpansion.scala
new file mode 100644
index 000000000..dffe8aca9
--- /dev/null
+++ b/src/dotty/tools/dotc/typer/EtaExpansion.scala
@@ -0,0 +1,109 @@
+package dotty.tools
+package dotc
+package typer
+
+import core._
+import ast.{Trees, untpd, tpd, TreeInfo}
+import Contexts._
+import Types._
+import Flags._
+import NameOps._
+import Symbols._
+import Decorators._
+import Names._
+import StdNames._
+import Trees._
+import util.Positions._
+import collection.mutable
+
+object EtaExpansion {
+
+  import tpd._
+
+  def lift(defs: mutable.ListBuffer[Tree], expr: Tree, prefix: String = "")(implicit ctx: Context): Tree =
+    if (TreeInfo.isIdempotentExpr(expr)) expr
+    else {
+      val name = ctx.freshName(prefix).toTermName
+      val sym = ctx.newSymbol(ctx.owner, name, EmptyFlags, expr.tpe, coord = positionCoord(expr.pos))
+      defs += ValDef(sym, expr)
+      Ident(sym.symRef)
+    }
+
+  def liftArgs(defs: mutable.ListBuffer[Tree], methType: Type, args: List[Tree])(implicit ctx: Context) = {
+    def toPrefix(name: Name) = if (name contains '$') "" else name.toString
+    def isByName(tp: Type) = tp.typeSymbol == defn.ByNameParamClass
+    val paramInfos = methType match {
+      case MethodType(paramNames, paramTypes) =>
+        (paramNames, paramTypes).zipped map ((name, tp) =>
+          (toPrefix(name), isByName(tp)))
+      case _ =>
+        args map Function.const(("", false))
+    }
+    for ((arg, (prefix, isByName)) <- args zip paramInfos)
+    yield
+      if (isByName) arg else lift(defs, arg, prefix)
+  }
+
+  def liftApp(defs: mutable.ListBuffer[Tree], tree: Tree)(implicit ctx: Context): Tree = tree match {
+    case Trees.Apply(fn, args) =>
+      tree.derivedApply(liftApp(defs, fn), liftArgs(defs, fn.tpe, args))
+    case Trees.TypeApply(fn, targs) =>
+      tree.derivedTypeApply(liftApp(defs, fn), targs)
+    case Trees.Select(pre, name) =>
+      tree.derivedSelect(lift(defs, pre), name)
+    case Trees.Ident(name) =>
+      lift(defs, tree)
+    case Trees.Block(stats, expr) =>
+      liftApp(defs ++= stats, expr)
+    case _ =>
+      tree
+  }
+
+  /** <p>
+   *    Expand partial function applications of type `type`.
+   *  </p><pre>
+   *  p.f(es_1)...(es_n)
+   *     ==>  {
+   *            <b>private synthetic val</b> eta$f   = p.f   // if p is not stable
+   *            ...
+   *            <b>private synthetic val</b> eta$e_i = e_i    // if e_i is not stable
+   *            ...
+   *            (ps_1 => ... => ps_m => eta$f([es_1])...([es_m])(ps_1)...(ps_m))
+   *          }</pre>
+   *  <p>
+   *    tree is already attributed
+   *  </p>
+  def etaExpandUntyped(tree: Tree)(implicit ctx: Context): untpd.Tree = { // kept as a reserve for now
+    def expand(tree: Tree): untpd.Tree = tree.tpe match {
+      case mt @ MethodType(paramNames, paramTypes) if !mt.isImplicit =>
+        val paramsArgs: List[(untpd.ValDef, untpd.Tree)] =
+          (paramNames, paramTypes).zipped.map { (name, tp) =>
+            val droppedStarTpe = defn.underlyingOfRepeated(tp)
+            val param = Trees.ValDef(
+              Trees.Modifiers(Param), name,
+              untpd.TypedSplice(TypeTree(droppedStarTpe)), untpd.EmptyTree)
+            var arg: untpd.Tree = Trees.Ident(name)
+            if (defn.isRepeatedParam(tp))
+              arg = Trees.Typed(arg, Trees.Ident(tpnme.WILDCARD_STAR))
+            (param, arg)
+          }
+        val (params, args) = paramsArgs.unzip
+        untpd.Function(params, Trees.Apply(untpd.TypedSplice(tree), args))
+    }
+
+    val defs = new mutable.ListBuffer[Tree]
+    val tree1 = liftApp(defs, tree)
+    Trees.Block(defs.toList map untpd.TypedSplice, expand(tree1))
+  }
+   */
+
+  def etaExpand(tree: Tree, tpe: MethodType)(implicit ctx: Context): Tree = {
+    def expand(tree: Tree): Tree = {
+      val meth = ctx.newSymbol(ctx.owner, nme.ANON_FUN, Synthetic, tpe, coord = tree.pos)
+      Closure(meth, Apply(tree, _))
+    }
+    val defs = new mutable.ListBuffer[Tree]
+    val tree1 = liftApp(defs, tree)
+    Block(defs.toList, expand(tree1))
+  }
+}
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